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For the purpose to understand the physical mechanism of noise which isimportant in photodiodes and photodetectors we setup a noise measurementmeasurement system to measure the noise performance of various devices andmaterials. The most important noise sources in semiconductor devices are thermalnoise, shot noise, generation-recombination noise and contact noise. Weanalyze the physical mechanism of the diffusion and generation-recombinationcurrent which both contribute to the noise in a diode and derive a universalformula of diode noise which can be written as 2qIA(V) where A(V) is the noise current gain. As long as we have the I-V characteristcs of a diode, according to this formula, we can calculate the theoretical noise currentgain and noise power and we don''t have to know the fraction of different current components in the diode. We design a low noise current preamplifier as the input stage of the noise measurement system and reduce the background current noise powerwhich improves the system performance. Then we measure the noise performanceof two commercial p-n diodes. The experimental data including noise powerand noise current gain all agree well with the theoretical value which proves the correctness of the theory.
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